// utility operators
template<typename T>
void cylinder(int nx, int ny, int nz, T dx, T cx, T cy, T cz, T r, T h, T v, T *f);
template<typename T>
void sphere(int nx, int ny, int nz, T dx, T cx, T cy, T cz, T r, T v, T *f);
template<typename T>
void rectangle(int nx, int ny, int nz, T dx, T cx, T cy, T cz, T w, T h, T d, T v, T *f);
